Abstract
Passive heat induces beneficial perfusion profiles, provides substantive cardiovascular strain, and reduces blood pressure, thereby holding potential for healthy and cardiovascular disease populations. The aim of this study was to assess acute responses to passive heat via lower-limb, hot-water immersion in patients with peripheral arterial disease (PAD) and healthy, elderly controls. Eleven patients with PAD (age 71 +/- 6 yr, 7 male, 4 female) and 10 controls (age 72 +/- 7 yr, 8 male, 2 female) underwent hotwater immersion (30-min waist-level immersion in 42.1 +/- 0.6 degrees C water). Before, during, and following immersion, brachial and popliteal artery diameter, blood flow, and shear stress were assessed using duplex ultrasound. Lower-limb perfusion was measured also using venous occlusion plethysmography and near-infrared spectroscopy. During immersion, shear rate increased (P < 0.0001) comparably between groups in the popliteal artery (controls: + 183 +/- 26%; PAD: + 258 +/- 54%) and brachial artery (controls: + 117 +/- 24%; PAD: + 107 +/- 32%). Lower-limb blood flow increased significantly in both groups, as measured from duplex ultrasound (> 200%), plethysmography (> 100%), and spectroscopy, while central and peripheral pulse-wave velocity decreased in both groups. Mean arterial blood pressure was reduced by 22 +/- 9 mmHg (main effect P < 0.0001, interaction P = 0.60) during immersion, and remained 7 +/- 7 mmHg lower 3 h afterward. In PAD, popliteal shear profiles and claudication both compared favorably with those measured immediately following symptom-limited walking. A 30-min hot-water immersion is a practical means of delivering heat therapy to PAD patients and healthy, elderly individuals to induce appreciable systemic (chronotropic and blood pressure lowering) and hemodynamic (upper and lower-limb perfusion and shear rate increases) responses.